They know Him in death. He judges them accoring to how they lived their lives, like He does the rest of us.
There is no place in hell for a good heart that gave love to others. God is so in love with His people, that whatever you do for one person, as far as He's concerned, you did it for Him.
There are so many reasons why someone would not know Christ while on earth. And Christ knows what each of them are.
But there's a difference between not knowing Him and actively trying to reject Him or make others reject Him.